Aqueous multicomponent polyurethane coating composition, process for its preparation and its use in methods of producing a multicoat finish

ABSTRACT

The present invention relates to an aqueous multicomponent polyurethane coating composition comprising 
     A) a water-dilutable polyaddition resin (A1) and/or polycondensation resin (A2) containing hydroxyl and carboxylate groups and having an OH number of from 40 to 200 mg of KOH/g, preferably from 60 to 140 mg of KOH/g, an acid number of from 15 to 100 mg of KOH/g, preferably from 25 to 50 mg of KOH/g, and a glass transition temperature of from -40° C. to +60° C., preferably from -20° C. to +40° C., 
     B) a polyisocyanate component (B) as crosslinking agent and 
     C) at least one additive, 
     characterized in that it contains as additive a carbodiimide component (C) which has a content of carbodiimide groups --N═C═N-- of from 2 to 30% by weight, on average at least 0.8 carbodiimide groups per molecule and from 0 to 25% by weight, based on solids, of chemically incorporated ethylene oxide and/or propylene oxide units which are present within polyether chains, 
     and/or a polyepoxide component (D).

The present invention relates to an aqueous multicomponent polyurethanecoating composition, comprising

A) a water-dilutable polyaddition resin (A1) and/or polycondensationresin (A2) containing hydroxyl and carboxylate and/or sulfonate groupsand having an OH number of from 40 to 200 mg of KOH/g, preferably from60 to 140 mg of KOH/g, an acid number of from 15 to 100 mg of KOH/g,preferably from 25 to 50 mg of KOH/g, and a glass transition temperatureof from -40° C. to +60° C., preferably from -20° C. to +40° C.,

B) a polyisocyanate component (B) as crosslinking agent and

C) at least one additive.

The present invention further relates to a process for the preparationof these aqueous coating compositions and to their use in methods ofproducing a multicoat finish, and to coated articles in which at leastone coat has been produced using these coating compositions.

For ecological and economic reasons the paint industry is making effortsto replace as great as possible a proportion of the organic solventswhich are employed in paints by water. Especially in automotivefinishing there is a great requirement for aqueous coatings. Thisapplies both to the sector of production-line (OEM) automotive finishingand to the sector of automotive refinishing.

In this context aqueous coating compositions are employed in particularin the area of top coats. Top coats are understood here as being coatingmaterials which are used to produce the topmost coat. This topmost coatmay comprise one or more coats, especially two coats. Two-coat top coatsare composed of a pigmented basecoat and of a clearcoat which ispigmented either not at all or only with transparent pigments and isapplied over the basecoat.

Two-coat finishes are currently produced by the wet-on-wet method, inwhich a pigmented basecoat is initially applied and the resultingbasecoat layer, without a baking step, is covered with a clearcoat, andthen basecoat layer and clearcoat layer are cured together. This methodis very advantageous in economic terms, but places stringentrequirements on the basecoat and the clearcoat.

The clearcoat which is applied to the as yet uncured basecoat mustneither partially dissolve nor otherwise perturb the basecoat layer,lest finishes of poor appearance be obtained. This applies in particularto finishes in which basecoats containing special-effect pigments (e.g.metallic pigments, especially aluminum flakes, or pearlescent pigments)are employed. Furthermore, the top coat compositions must be capable ofbeing applied by spraying using automatic coating units. For thispurpose their solids content at spray viscosity must be high enough forcoating films of adequate thickness to be obtained with 1 to 2 spraypasses (cross passes), and they must give baked coating films of goodappearance (good evenness, high gloss, good top coat holdout and a highdegree of hardness) and good weathering resistance.

In the area of automotive refinishing there is the additionalrequirement that the coating compositions employed are able to curefully at low temperatures (generally <80° C.) and lead, even when fullycured at these low temperatures, to films having the good mechanicalproperties required.

EP-B-358 979 discloses aqueous two-component polyurethane coatingcompositions which comprise a hydroxyl group-containing polyacrylateresin and a polyisocyanate component. However, these coatings describedin EP-B-358 979 exhibit great disadvantages with respect to weatheringresistance, in particular with respect to their resistance in a constanthumid climate (40° C., 240 h), and processability (fall in viscosity andtoo short pot life).

It is furthermore known, from EP-B-198 343, to add isocyanatederivatives containing carbodiimide groups to aqueous solutions ofpolymers which contain carboxyl groups, to improve the mechanicalproperties, especially the wet strength. However, when the carbodiimidesdescribed in EP-B-198 343 are used in aqueous polyurethane coatingcompositions, problems of compatibility with the binders occur and theresulting coatings have an inadequate weathering stability.

Moreover, EP-A-121 083 describes crosslinking agents based oncarbodiimides, which are employed to crosslink aqueous resins containingcarboxyl groups. The addition of carbodiimides to polyurethane coatingcompositions is not described in EP-A-121 083. Furthermore, thecarbodiimides described in EP-A-121 083 are not polyether-modified.Rather, they are incorporated into aqueous dispersions using emulsifiersand water-miscible solvents.

In addition, EP-A-507 407 discloses coating compositions which containas crosslinking agents carbodiimides which contain not only carbodiimidegroups but also crosslinkable groups. By this means it is possible toavoid using a further crosslinking agent. The coating compositions knownfrom EP-A-507 407 have the disadvantage, however, that their preparationis more time-consuming and cost-intensive than the mixing of differentcrosslinking agents having different functional groups. These coatingcompositions also have the disadvantage of a high VOC (Volatile OrganicContent), since the processing of the coating compositions requirestheir dilution with organic solvents to a solids content of 50%.Furthermore, EP-A-507 407 contains no information on the short-termweathering stability of the coatings.

Finally, EP-A-516 277 discloses aqueous two-component polyurethanecoatings which contain, as the component which is essential to theinvention, a polyether-modified polyisocyanate. As binders these aqueoustwo-component coatings contain polyacrylate resins which areconventionally employed. The use of polyether-modified polyisocyanateshas the disadvantage, however, that the resulting coatings have only alow weathering stability, and in particular poor results in the constanthumid climate test.

The present invention is therefore based on the object of providingaqueous multicomponent polyurethane coating compositions of the typementioned initially which, in relation to the known aqueous polyurethanecoating compositions, have improved properties and/or give improvedcoating films. The new coating compositions should above all have animproved weathering stability. Despite hybrid crosslinking using two ormore different crosslinking agents, the coating compositions shouldmoreover possess the same ease of application as conventional2-component PUR coating compositions.

The new coating compositions should also be suited to the area ofautomotive refinishing, i.e. they should be able to cure fully at lowtemperatures (generally <80° C.) and should lead to coatings which meetat least the requirements conventionally placed on an automotiverefinish. The coating compositions should therefore have, for example,good evenness and good mechanical properties.

Surprisingly this object has been achieved by aqueous multicomponentpolyurethane coating compositions of the type mentioned initially, whichare characterized in that they contain as additive a carbodiimidecomponent (C) which has a content of carbodiimide groups --N═C═N-- offrom 2 to 30% by weight, on average at least 0.8 carbodiimide groups permolecule and from 0 to 25% by weight, based on solids, of chemicallyincorporated ethylene oxide and/or propylene oxide units which arepresent within polyether chains, and/or a polyepoxide component (D).

The present invention relates furthermore to a process for thepreparation of the aqueous multicomponent polyurethane coatingcompositions in which, shortly before application, a component whichcomprises the isocyanate group-containing crosslinking agent and thecarbodiimide component is mixed with the component which comprises thewater-dilutable binder. The invention also relates to a method ofproducing a multilayer, protective and/or decorative coating on asubstrate surface, in which the top coat composition employed comprisesthe aqueous coating compositions according to the invention, and to thecoated articles obtained by this method. Finally, the present inventionalso relates to the use of the aqueous coating compositions.

It is surprising and was unforeseeable that the aqueous polyurethanecoating compositions obtained by using the carbodiimide component and/orthe polyepoxide component, which is or are employed in accordance withthe invention, have an improved weathering stability (i.e. goodresistance in the constant humid climate test and in the water spraytest). A further advantage is that the coating compositions according tothe invention exhibit better leveling than conventional 2-component PURcoating compositions and that the coating compositions according to theinvention possess the same ease of application as conventional2-component PUR coating compositions.

A further advantage, finally, is that the coating compositions lead tocoatings having good mechanical properties.

In the text below a closer description will first be given of theindividual components of the aqueous coating composition according tothe invention. Before the preparation of the polyacrylate resins to beemployed in accordance with the invention is described more closely, twoexplanations of terms are dealt with beforehand:

1. (Meth)acrylic acid is occasionally used as an abbreviation for"methacrylic acid or acrylic acid".

2. The formulation "essentially free from carboxyl groups" is intendedto express the fact that components (a1), (a2), (a4), (a5) and (a6) mayhave a small carboxyl group content (but no more than would give apolyacrylate resin prepared from these components a maximum acid numberof 10 mg of KOH/g). It is preferred, however, for the carboxyl groupcontent of components (a1), (a2), (a4), (a5) and (a6) to be kept as lowas possible. It is particularly preferred to employ carboxyl group-freecomponents (a1), (a2), (a4), (a5) and (a6).

The coating compositions according to the invention contain as binder awater-dilutable polyaddition resin (A1) and/or polycondensation resin(A2) which contains hydroxyl and carboxylate and/or sulfonate groups andhas an OH number of from 40 to 200 mg of KOH/g, preferably from 60 to140 mg of KOH/g, an acid number of from 15 to 100 mg of KOH/g,preferably from 25 to 50 mg of KOH/g, and a glass transition temperatureof from -40° C. to +60° C., preferably from -20° C. to +40° C.

The polycondensation resins which are suitable as binders are knownperse sic! and are described in, for example, EP-A-542 105. Polyesterresins are preferably employed as (A2). The sulfonate groups can beintroduced into the polyester by using, for example,5-(lithiumsulfo)isophthalic acid.

Polyacrylate resins are preferably employed as binders in the coatingcompositions according to the invention. These polyacrylate resins arepreferably prepared by polymerizing, in an organic solvent or solventmixture and in the presence of at least one polymerization initiator,

a1) a (meth)acrylate which is different from (a2), (a3), (a4), (a5) and(a6), is copolymerizable with (a2), (a3), (a4), (a5) and (a6) and isessentially free from carboxyl groups, or a mixture of such monomers,

a2) an ethylenically unsaturated monomer which is copolymerizable with(a1), (a2) sic!, (a3), (a4), (a5) and (a6), is different from (a5),carries at least one hydroxyl group per molecule and is essentially freefrom carboxyl groups, or a mixture of such monomers,

a3) an ethylenically unsaturated monomer which carries at least onecarboxyl group and/or sulfonate group per molecule and iscopolymerizable with (a1), (a2), (a4), (a5) and (a6), or a mixture ofsuch monomers, and

a4) if desired one or more vinyl esters of α-branched monocarboxylicacids having from 5 to 18 carbon atoms per molecule, and/or

a5) if desired at least one reaction product of acrylic acid and/ormethacrylic acid with the glycidyl ester of an α-branched monocarboxylicacid having from 5 to 18 carbon atoms per molecule, or, instead of thereaction product, an equivalent amount of acrylic and/or methacrylicacid which is then reacted during or after the polymerization reactionwith the glycidyl ester of an α-branched monocarboxylic acid having from5 to 18 carbon atoms per molecule,

a6) if desired an ethylenically unsaturated monomer which iscopolymerizable with (a1), (a2), (a3), (a4) and (a5), is different from(a1), (a2), (a4) and (a5) and is essentially free from carboxyl groups,or a mixture of such monomers,

and, after the end of the polymerization, at least partiallyneutralizing the resulting polyacrylate resin and dispersing it inwater, the nature and quantity of (a1), (a2), (a3), (a4), (a5) and (a6)being selected such that the polyacrylate resin (A1) has the desired OHnumber, acid number and glass transition temperature.

The preparation of the polyacrylate resins which are employed inaccordance with the invention may employ as component (a1) any ester of(meth)acrylic acid which is copolymerizable with (a2), (a3), (a4), (a5)and (a6) and is essentially free from carboxyl groups, or a mixture ofsuch (meth)acrylates. Examples are alkyl acrylates and alkylmethacrylates having up to 20 carbon atoms in the alkyl radical, forexample methyl, ethyl, propyl, butyl, hexyl, ethylhexyl, stearyl andlauryl acrylate and methacrylate, and cycloaliphatic (meth)acrylatessuch as cyclohexyl methacrylate. It is preferred to employ as component(a1) mixtures of alkyl acrylates and/or alkyl methacrylates, of which atleast 20% by weight are composed of n-butyl and/or t-butyl acrylateand/or n-butyl and/or t-butyl methacrylate.

As component (a1) it is also possible to employ ethyltriglycol(meth)acrylate and methoxyoligoglycol (meth)acrylate having anumber-average molecular weight of preferably 550 or other ethoxylatedand/or propoxylated derivatives of (meth)acrylic acid which are freefrom hydroxyl groups.

As component (a2) it is possible to employ ethylenically unsaturatedmonomers which are copolymerizable with (a1), (a2) sic!, (a3), (a4),(a5) and (a6), are different from (a5), carry at least one hydroxylgroup per molecule and are essentially free from carboxyl groups, or amixture of such monomers. Examples are hydroxyalkyl esters of acrylicacid, methacrylic acid or another α,β-ethylenically unsaturatedcarboxylic acid. These esters may be derived from an alkylene glycolwhich is esterified with the acid, or they may be obtained by reactingthe acid with an alkylene oxide. As component (a2) it is preferred toemploy hydroxyalkyl esters of acrylic acid or methacrylic acid in whichthe hydroxyalkyl group contains up to 20 carbon atoms, reaction productsof cyclic esters, e.g. ε-caprolactone, and these hydroxyalkyl esters, ormixtures of these hydroxyalkyl esters and/or ε-caprolactone-modifiedhydroxyalkyl esters.

Examples of such hydroxyalkyl esters are 2-hydroxyethyl acrylate,2-hydroxypropyl acrylate, 3-hydroxypropyl acrylate, 2-hydroxypropylmethacrylate, 3-hydroxypropyl methacrylate, 2-hydroxyethyl methacrylate,4-hydroxybutyl acrylate, 4-hydroxybutyl methacrylate, hydroxystearylacrylate and hydroxystearyl methacrylate. Corresponding esters of otherunsaturated acids, for example ethacrylic acid, crotonic acid andsimilar acids having up to about 6 carbon atoms per molecule, can alsobe employed. It is also possible to employ olefinically unsaturatedpolyols as component (a2). Preferred polyacrylate resins (A) areobtained when trimethylolpropane monoallyl ether is employed as at leastpart of component (a2). The proportion of trimethylolpropane monoallylether is usually from 2 to 10% by weight, based on the total weight ofthe monomers (a1) to (a6) employed in the preparation of polyacrylateresin. In addition, however, it is also possible to add from 2 to 10% byweight, based on the total weight of the monomers employed in thepreparation of the polyacrylate resin, of trimethylolpropane monoallylether to the finished polyacrylate resin. The olefinically unsaturatedpolyols such as, in particular, trimethylolpropane monoallyl ether maybe employed as the sole hydroxyl group-containing monomer, but areemployed in particular in proportions in combination with other of thehydroxyl group-containing monomers mentioned.

As component (a3) any ethylenically unsaturated monomer which carries atleast one sulfonyl and/or carboxyl group per molecule and iscopolymerizable with (a1), (a2), (a4), (a5) and (a6), or a mixture ofsuch monomers, can be employed. It is preferred to employ acrylic acidand/or methacrylic acid as component (a3). However, it is also possibleto employ other ethylenically unsaturated acids having up to 6 carbonatoms in the molecule. Examples of such acids are ethacrylic acid,crotonic acid, maleic acid, fumaric acid and itaconic acid. It is alsopossible to employ as component (a3) mono(meth)acryloyloxyethyl maleate,mono(meth)acryloyloxyethyl succinate and mono(meth)acryloyloxyethylphthalate. Examples of monomers containing sulfonyl groups are2-acrylamido-2-methylpropanesulfonic acid and vinylsulfonic acid.

As component (a4) one or more vinyl esters of α-branched monocarboxylicacids having from 5 to 18 carbon atoms in the molecule are employed. Thebranched monocarboxylic acids can be obtained by reacting formic acid orcarbon monoxide and water with olefins in the presence of a liquid,strongly acid catalyst; the olefins may be products from the cracking ofparaffinic hydrocarbons such as mineral oil fractions, and may containboth branched and straight-chain acyclic and/or cycloaliphatic olefins.The reaction of such olefins with formic acid or with carbon monoxideand water produces a mixture of carboxylic acids in which the carboxylgroups are predominantly located on a quaternary carbon atom. Examplesof other olefinic starting substances are propylene trimer, propylenetetramer and diisobutylene. The vinyl esters may, however, also beprepared from the acids in a manner known per se, for example byreacting the acid with acetylene.

Because of their ready availability, it is particularly preferred toemploy vinyl esters of saturated aliphatic monocarboxylic acids havingfrom 9 to 11 carbon atoms, which are branched on the α carbon atom.

As component (a5) the reaction product of acrylic acid and/ormethacrylic acid with the glycidyl ester of an α-branched monocarboxylicacid having from 5 to 18 carbon atoms per molecule is employed. Glycidylesters of strongly branched monocarboxylic acids can be obtained underthe trade name "Cardura". The acrylic or methacrylic acid can be reactedwith the glycidyl ester of a carboxylic acid having a tertiary α carbonatom before, during or after the polymerization reaction. Preference isgiven to employing as component (a5) the reaction product of acrylic andof methacrylic acid with the glycidyl ester of Versatic acid. Thisglycidyl ester is commercially available under the name "Cardura E10".

As component (a6) it is possible to employ all ethylenically unsaturatedmonomers which are copolymerizable with (a1), (a2), (a3), (a4) and (a5),are different from (a1), (a2), (a3) and (a4) and are essentially freefrom carboxyl groups, or mixtures of such monomers. Preferably employedas component (a6) are vinyl aromatic hydrocarbons such as styrene,α-alkylstyrene and vinyltoluene.

As component (a6) it is also possible to employ, in combination withother monomers mentioned as being suitable as component (a6),polysiloxane macromonomers. Suitable polysiloxane macromonomers arethose having a number-average molecular weight of from 1000 to 40,000,preferably from 2000 to 10,000, and on average from 0.5 to 2.5 andpreferably 0.5 to 1.5 ethylenically unsaturated double bonds permolecule. Suitable examples are the polysiloxane macromonomers describedin DE-A-38 07 571 on pages 5 to 7, in DE-A-37 06 095 in columns 3 to 7,in EP-B 358 153 on pages 3 to 6 and in U.S. Pat. No. 4,754,014 incolumns 5 to 9. Also suitable, furthermore, are otheracryloxysilane-containing vinyl monomers having the abovementionedmolecular weights and contents of ethylenically unsaturated doublebonds, for example compounds which can be prepared by reactinghydroxy-functional silanes with epichlorohydrin and subsequentlyreacting the reaction product with methacrylic acid and/or hydroxyalkylesters of (meth)acrylic acid.

Preferred polysiloxane macromonomers for employment as component (a6)are those of the following formula: ##STR1## where R¹ ═H or CH₃

R², R³, R⁴, R⁵ =identical or different aliphatic hydrocarbon radicalshaving from 1 to 8 carbon atoms, especially methyl, or a phenyl radical.

n=from 2 to 5, preferably 3

m=from 8 to 30

Particular preference is given to employing the α, -acryloxy sic!organo-functional polydimethyl-siloxane of the formula ##STR2## wheren≈9, with an acryloxy equivalent of 550 g per equivalent, an OH numberof 102 mg of KOH/g and a viscosity of 240 mPas (25° C.).

Also preferably employed as component (a6) are polysiloxanemacromonomers which have been prepared by reacting from 70 to 99.999mol-% of a compound (1), represented by the formula (I) ##STR3## inwhich R¹ represents an aliphatic hydrocarbon group having from 1 to 8carbon atoms or a phenyl radical and R², R³ and R⁴ each represent ahalogen radical or an alkoxy radical having 1 to 4 carbon atoms, or ahydroxyl group, with from 30 to 0.001 mol-% of a compound (2),represented by the formula (II) ##STR4## in which R⁵ represents ahydrogen atom or a methyl radical, R⁶, R⁷ and R⁸ each represent halogen,OH-- or an alkoxy radical having from 1 to 4 carbon atoms, or analiphatic hydrocarbon group having from 1 to 8 carbon atoms, at leastone of the radicals R⁶, R⁷ or R⁸ representing OH-- or an alkoxy groupand n representing an integer from 1 to 6.

Examples of suitable compounds (1) and (2) are mentioned in WO 92/22615on page 13, line 18 to page 15, line 9.

The reaction between compounds (1) and (2) is brought about by thedehydrating condensation of the hydroxyl groups which these compoundscontain and/or the hydroxyl groups which can be attributed to thehydrolysis of the alkoxy groups in these compounds. Depending on thereaction conditions the reaction comprises in addition to thedehydration reaction a dealcohalizing sic! condensation. If compounds(1) or (2) contain halogen radicals the reaction between (1) and (2) isbrought about by dehydrohalogenation.

The conditions under which the reaction between compound (1) andcompound (2) is carried out are likewise described in the internationalpatent application having the international publication no. WO 92/22615on page 15, line 23 to page 18, line 10.

The amount of the polysiloxane macromonomer(s) (a6) employed to modifythe acrylate copolymers (A1) is less than 5% by weight, preferably from0.05 to 2.5% by weight and particularly preferably from 0.05 to 0.8% byweight, based in each case on the total weight of the monomers employedin the preparation of the copolymer (A1).

The use of such polysiloxane macromonomers leads to an improvement inthe slip of the aqueous polyurethane coating composition.

The nature and quantity of components (a1) to (a6) is selected such thatthe polyacrylate resin (A1) has the desired OH number, acid number andglass transition temperature. Particular preference is given toemploying acrylate resins obtained by polymerizing

(a1) from 20 to 60% by weight, preferably from 30 to 50% by weight, ofcomponent (a1)

(a2) from 10 to 40% by weight, preferably from 15 to 35% by weight, ofcomponent (a2)

(a3) from 1 to 15% by weight, preferably from 2 to 8% by weight, ofcomponent (a3) and

(a4) from 0 to 25% by weight, preferably from 2 to 15% by weight, ofcomponent (a4)

(a5) from 0 to 25% by weight, preferably from 2 to 15% by weight, ofcomponent (a5)

(a6) from 5 to 30% by weight, preferably from 10 to 20% by weight, ofcomponent (a6),

the sum of the proportions by weight of components (a1) to (a6) being ineach case 100% by weight.

The polyacrylate resins (A1) employed in accordance with the inventionare prepared in an organic solvent or solvent mixture and in thepresence of at least one polymerization initiator. The organic solventsand polymerization initiators employed are those solvents andpolymerization initiators which are conventional for the preparation ofpolyacrylate resins and suitable for the preparation of aqueousdispersions. Examples of solvents which can be used are butylglycol,2-methoxypropanol, n-butanol, methoxybutanol, n-propanol, ethyleneglycol monomethyl ether, ethylene glycol monoethyl ether, ethyleneglycol monobutyl ether, diethylene glycol monomethyl ether, diethyleneglycol monoethyl ether, diethylene glycol diethyl ether, diethyleneglycol monobutyl ether, ethyl 2-hydroxypropionate and3-methyl-3-methoxybutanol, and derivatives based on propylene glycol,for example ethyl ethoxypropionate, methoxypropyl acetate, dipropyleneglycol monomethyl ether and the like. Examples of polymerizationinitiators which can be used are free radical initiators such as, forexample, t-butyl perethylhexanoate, benzoyl peroxide,azobisisobutyronitrile and t-butyl perbenzoate. The polymerization isexpediently carried out at a temperature of from 80° to 160° C.,preferably from 110° to 160° C. The preferred solvents employed areethoxyethyl propionate, dipropylene glycol monomethyl ether and butylacetate.

The polyacrylate resin (A1) is preferably prepared by a two-stageprocess, since in this way the resulting aqueous coating compositionshave a better processability. Preference is therefore given to employingpolyacrylate resins which can be obtained by

I. polymerizing a mixture of (a1), (a2), (a4), (a5) and (a6), or amixture of part-amounts of components (a1), (a2), (a4), (a5) and (a6) inan organic solvent,

II. after at least 60% by weight of the mixture composed of (a1), (a2),(a4), (a5) and if desired (a6) have been added, adding (a3) and anyremaining amount of components (a1), (a2), (a4), (a5) and (a6) andcontinuing polymerization, and

III. after the end of the polymerization, at least partiallyneutralizing the resulting polyacrylate resin and dispersing it inwater.

In addition, however, it is also possible initially to charge components(a4) and/or (a5) together with at least a part-amount of the solvent andto meter in the remaining components. Furthermore it is also possible toinclude in the initial charge only part of components (a4) and/or (a5)together with at least part of the solvent, and to add the remainder ofthese components as described above. It is preferred, for example,initially to charge at least 20% by weight of the solvent and about 10%by weight of components (a4) and (a5) and if desired part-amounts ofcomponents (a1) and (a6).

Also preferred is the preparation of the polyacrylate resins (A1) whichare employed in accordance with the invention by a two-stage process inwhich stage (I) lasts from 1 to 8 hours, preferably from 1.5 to 4 hours,and the addition of the mixture of (a3) and any remaining amounts ofcomponents (a1), (a2), (a4), (a5) and (a6) is made over a period of from20 to 120 min, preferably over a period of from 30 to 90 min. When theaddition of the mixture of (a3) and any remaining amounts of components(a1), (a2), (a4), (a5) and (a6) is complete polymerization is continueduntil all of the monomers employed have undergone essentially completereaction.

The quantity and rate of addition of the initiator is preferably chosensuch that a polyacrylate resin (A1) having a number-average molecularweight of from 2500 to 20,000 is obtained. It is preferred to commencethe addition of the initiator about 5 minutes before adding the monomersand to terminate it about half an hour after the addition of themonomers has been ended. The initiator is preferably added in a constantquantity per unit time. When the addition of initiator has ended thereaction mixture is maintained at polymerization temperature for a time(generally 11/2 h) until all the monomers employed have undergoneessentially complete reaction. "Essentially complete reaction" isintended to denote that preferably 100% by weight of the monomersemployed have been reacted, but that it is also possible for a smallproportion of residual monomer of no more than up to about 0.5% byweight, based on the weight of the reaction mixture, possibly to remainunreacted.

The resulting polyacrylate resin (A1) has an OH number of from 40 to 200and preferably from 60 to 140 mg of KOH/g, an acid number of from 20 to100 mg of KOH/g, preferably from 25 to 50 mg of KOH/g, and a glasstransition temperature of from -40° to +60° C., preferably from -20° to+40° C. This glass transition temperature can be calculated by thefollowing formula: ##EQU1##

Tg=glass transition temperature of the polyacrylate resin (A)

X=number of different monomers copolymerized in the polyacrylate resin

Wn=weight proportion of the nth monomer

Tgn=glass transition temperature of the homopolymer of the nth monomer

For calculating the glass transition temperature the Tg of thehomopolymer of the reaction product of acrylic acid and Cardura E10 istaken to be equal to the glass transition temperature of the homopolymerof isodecyl methacrylate (-41° C.).

When the polymerization is over the resulting polyacrylate resin is atleast partially neutralized and dispersed in water. The degree ofneutralization to be applied in each case depends on the acid number ofthe acrylate and is in general, for acid numbers <70 mg of KOH/g,between 50 and 90% and, for acid numbers >70 mg of KOH/g, between 30 and80%. Both organic bases and inorganic bases can be used for theneutralization. It is preferred to use primary, secondary and tertiaryamines such as, for example, ethylamine, propylamine, dimethylamine,dibutylamine, cyclohexylamine, benzylamine, morpholine, piperidine,diethanolamine and triethanolamine. It is particularly preferred toemploy tertiary amines as neutralizing agents, in particulardimethylethanolamine, triethylamine, dimethylisopropylamine,tripropylamine and tributylamine.

The neutralization reaction is generally carried out by mixing theneutralizing base with the polyacrylate resin. In this context it ispreferred to employ a quantity of base such that the top coatcomposition has a pH of from 7 to 8.5, preferably from 7.2 to 7.8.

The partially or completely neutralized polyacrylate resin is thendispersed by adding water. This produces an aqueous polyacrylate resindispersion. If desired some or all of the organic solvent can bedistilled off. The polyacrylate resin dispersions according to theinvention contain polyacrylate resin particles whose average size ispreferably between 60 and 300 nm (method of measurement: laserdiffraction; measuring instrument: Malvern Autosizer 2 C). Thepolyacrylate resin (A1) employed in accordance with the invention isconventionally employed in the coating compositions in an amount of from30 to 50% by weight (calculated as solids, i.e. without the watercontent), based on the total weight of the coating composition.

The polyisocyanate component (B) is any organic polyisocyanate havingfree isocyanate groups which are bonded to aliphatic, cycloaliphatic,araliphatic and/or aromatic structures. Preferably employed arepolyisocyanates having from 2 to 5 isocyanate groups per molecule andhaving viscosities of from 200 to 2000 mPas (at 23° C.). If desiredsmall amounts of organic solvent may also be added to thepolyisocyanates, preferably from 1 to 25% based on pure polyisocyanate,in order thus to improve the ease of incorporation of the isocyanate andif appropriate to reduce the viscosity of the polyisocyanate to a valuewithin the abovementioned ranges. Examples of solvents which aresuitable as additives for the polyisocyanates are ethoxyethylpropionate, butyl acetate and the like.

Examples of suitable isocyanates are described by way of example in"Methoden der organischen Chemie", Houben-Weyl, volume 14/2, 4thedition, Georg Thieme Verlag, Stuttgart 1963, page 61 to 70, and by W.Siefken, Liebigs Ann. Chem. 562, 75 to 136. Suitable examples are1,2-ethylene diisocyanate, 1,4-tetramethylene diisocyanate,1,6-hexamethylene diisocyanate, 2,2,4- or2,4,4-trimethyl-1,6-hexamethylene diisocyanate, 1,12-dodecanediisocyanate, ω,ω'-diisocyanatodipropyl ether, cyclobutane1,3-dilsocyanate, cyclohexane 1,3- and 1,4-diisocyanate, 2,2- and2,6-diisocyanato-1-methylcyclo-hexane,3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (isophoronediisoyanate" sic!), 2,5- and3,5-bis(isocyanatomethyl)-8-methyl-1,4-methano-decahydronaphthalene,1,5-, 2,5-, 1,6- and2,6-bis(iso-cyanatomethyl)-4,7-methanohexahydroindane, 1,5-, 2,5-, 1,6-and 2,6-bis(isocyanato)-4,7-methanehexahydro-indane, dicyclohexyl 2,4'-and 4,4'-diisocyanate, 2,4-and 2,6-hexahydrotolylene diisocyanate,perhydro-2,4'-and -4,4'-diphenylmethane diisocyanate,ω,ω'-diisocya-nato-1,4-diethylbenzene, 1,3- and 1,4-phenylenediisocyanate, 4,4'-diisocyanato-biphenyl,4,4'-diisocy-anato-3,3'-dichlorobiphenyl,4,4'-diisocyanato-3,3'-dimethoxy-biphenyl,4,4'-diisocyanato-3,3'-dimethylbiphenyl,4,4'-diisocyanato-3,3'-diphenyl-biphenyl, 2,4'- and4,4'-diisocyanato-diphenylmethane, naphthylene 1,5-diisocyanate,tolylene diisocyanates such as 2,4- and 2,6-tolylene diisocyanate,N,N'-(4,4'-dimethyl-3,3'-diisocyanatodiphenyl)uretdione, mxylylenediisocyanate, dicyclohexylmethane diisocyanate, tetramethylxylylenediisocyanate, but also triisocyanates such as2,4,4'-triisocyanatodiphenyl ether and4,4',4"-triisocyanatotriphenylmethane. It is also possible to employpolyisocyanates having isocyanurate groups and/or biuret groups and/orallophanate groups and/or urethane groups and/or urea groups.Polyisocyanates having urethane groups are obtained, for example, byreacting some of the isocyanate groups with polyols such as, forexample, trimethylolpropane and glycerol.

Aliphatic or cycloaliphatic polyisocyanates are preferably employed,especially hexamethylene diisocyanate, dimerized and trimerizedhexamethylene diisocyanate, isophorone diisocyanate,dicyclohexyl-methane 2,4'-diisocyanate or dicyclohexylmethane4,4'-diisocyanate or mixtures of these polyisocyanates. Very particularpreference is given to employing mixtures of polyisocyanates based onhexamethylene diisocyanate which contain uretdione and/or isocyanurategroups and/or allophanate groups, as are formed by catalyticoligomerization of hexamethylene diisocyanate using suitable catalysts.Polyisocyanate component (B) may otherwise be composed of any desiredmixtures of the polyisocyanates mentioned by way of example.

It is essential to the invention that the coating compositions contain acarbodiimide component (C) and/or a polyepoxide component (D). Thecoating compositions preferably contain a carbodiimide component (C) ora mixture of a carbodiimide component (C) and a polyepoxide component(D). The carbodiimide component (C) which is employed may in each casebe a carbodiimide or else a mixture of 2 or more carbodiimides.Likewise, the polyepoxide component (D) which is employed may in eachcase be a polyepoxide or a mixture of 2 or more polyepoxides.

The carbodiimides which are employed in accordance with the inventionhave the following characteristic properties:

1. The incorporation of hydrophilic ethylene oxide and/or propyleneoxide units enables the carbodiimides employed in accordance with theinvention to be added without problems to aqueous solutions and, inparticular, dispersions of synthetic resins containing carboxylateand/or carboxyl groups and/or sulfonate groups.

2. In dependence on the content of carbodiimide groups in thecarbodiimide component employed in accordance with the invention, whichcontent can easily be varied by a simple choice of the nature andproportions of the starting materials employed, the degree ofcrosslinking of the two-dimensional structure ultimately obtained can beadjusted.

Starting materials for the carbodiimides employed in accordance with theinvention are:

a) organic polyisocyanates having an average NCO functionality of from2.0 to 2.5 or mixtures of organic poly- and monoisocyanates having anaverage functionality of from 1.3 to 2.5 and, if desired,

b) compounds which are mono- or polyfunctional in terms of theisocyanate addition reaction and have groups which are reactive towardisocyanate groups.

Structural components a) include:

a1) any desired aliphatic and/or cycloaliphatic and/or aromaticpolyisocyanates such as, in particular, the diisocyanates which areeasily accessible industrially such as hexamethylene diisocyanate,1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcy-clohexane andm-tetramethylenexylylene diisocyanate (m-TMXDI).

If aromatic polyisocyanates are employed then it is preferred to employthose in which the isocyanate groups are bonded to aliphatic radicals.Particularly preferred isocyanates for preparing the carbodiimides arethose of the general formula (I) ##STR5## in which X represents adivalent, aromatic hydrocarbon radical, preferably for a naphthylene,diphenylene or 1,2-, 1,3- or 1,4-phenylene radical which is optionallysubstituted by halogen, methyl or methoxy, particularly preferably a1,3-phenylene radical, and R₁ and R₂ represent an alkyl radical having1-4 carbon atoms, preferably a methyl radical. Diisocyanates of theformula (I) are known (their preparation is described in, for example,EP-A-101 832, U.S. Pat. Nos. 3,290,350, 4,130,577 and 4,439,616) andsome are commercially available (1,3-bis-(2-isocyanatoprop-2-yl)benzenefor example is sold by the American Cyanamid Company under the tradename TMXDI (META)®).

The exclusive employment is preferred, as component (a1), of adiisocyanate of the formula (I) or a mixture of such diisocyanates. Itis particularly preferred to employ as component (a1) a diisocyanate ofthe formula (II) ##STR6## These isocyanates are also designated astetramethylxylylene diisocyanates (TMXDI). Very particular preference isgiven to the employment as component (a1) of a diisocyanate of theformula (II) in which the --C(CH3)₂ NCO groups are in the meta position(MTMXDI).

Further starting materials (a) are:

a2) Hydrophilically modified polyisocyanates.

These include mono- or diisocyanates which contain polyethylene oxideand/or polypropylene oxide units incorporated within polyether chains,as are described in, for example, DE-A-23 14 512, DE-A-23 14 513,DE-A-25 51 094, DE-A-26 51 506, U.S. Pat. Nos. 3,920,598 or 3,905,929.

Particularly preferred hydrophilically modified polyisocyanates,however, are NCO prepolymers as are obtained by reacting excess amountsof the diisocyanates mentioned as examples under a1) with diols. In thepreparation of these NCO prepolymers the starting materials aregenerally brought to reaction while observing a ratio of NCO to OHequivalents of from 1.2:1 to 10:1 at from 20° to 150° C.

Diols which are suitable for the preparation of NCO prepolymers are inparticular those of the general formula ##STR7## in which A and Brepresent identical or different divalent aliphatic hydrocarbon radicalshaving from 1 to 6 carbon atoms, R represents hydrogen, an aliphatichydrocarbon radical having from 1 to 4 carbon atoms or a phenyl radical,n and m represent identical or different numbers from 0 to 30 and o andp each represent 0 or 1.

Further starting materials (a) are, for example:

a3) organic monoisocyanates, such as, for example, n-hexyl isocyanate,phenyl isocyanate or p-tolyl isocyanate. As already mentioned abovethese monoisocyanates are possibly employed as a mixture with organicpolyisocyanates of the kind mentioned by way of example, the mixturehaving an average NCO functionality of from 1.3 to 2.5, preferably from1.3 to 2.

In addition, other modified polyisocyanates may also be present incomponent (a), for example reaction products of excess amounts oforganic diisocyanates of the kind mentioned by way of example under (a1)with di- or trihydroxyalkanes having a molecular weight of less than400, for example ethylene glycol, propylene glycol, tetramethylenediols, hexamethylene diols, trimethylolpropane and/or glycerol.

Examples of the structural components (b) which are also used if desiredare

b1) polyhydric, especially dihydric alcohols, for example ethyleneglycol, propylene glycol, tetramethylene diols, hexamethylene diols,octamethylene diols, neopentyl glycol, 2-methyl-1,3-dihydroxypropane,glycerol, trimethylolpro-pane, diethylene glycol, triethylene glycol,tetraethylene glycol, polyethylene glycols of the molecular weightsmentioned, dipropylene glycol, tripropylene glycol or any desiredmixtures of such polyhydric alcohols.

It is preferred to employ methoxypolyethylene glycol having an averagemolecular weight of 550 g/mol with 1 free OH group and 1methyl-etherified OH group.

Examples of further structural components (b) which are also used ifdesired are:

b2) Hydrophilically modified mono- or dihydric alcohols, for example thecompounds which have ethylene oxide units and the general formula##STR8## in which

R lacuna! a divalent radical as obtained by removing the isocyanategroups from a diisocyanate of the formula R(NCO)2 of the kind mentionedabove under (a1),

R' lacuna! hydrogen or a monovalent hydrocarbon radical having 1-8carbon atoms, preferably hydrogen or a methyl group,

R" lacuna! a monovalent hydrocarbon radical having 1-12 carbon atoms,preferably an unsubstituted alkyl radical having 1-4 carbon atoms,

X lacuna! a polyalkylene oxide chain having 5-90 and preferably 20 to 70chain members of which at least 40%, preferably at least 65%, arecomposed of ethylene oxide units and which in addition to ethylene oxideunits may also represent propylene oxide, butylene oxide or styreneoxide units, with propylene oxide units being preferred among thelast-mentioned units,

Y lacuna! oxygen or --NR'"--, where R'" in terms of its definitioncorresponds to R".

The compounds of the abovementioned formulae may be prepared inaccordance with the procedures of DE-A-23 14 512 and/or DE-A-23 14 513;in order to supplement the disclosure made therein reference is made tothe fact that, instead of the monofunctional polyether alcoholsmentioned therein as starting material, it is also possible to employthose polyether alcohols whose polyether segment also has, in additionto ethylene oxide units, 60% by weight based on the polyether segment ofa sic! propylene oxide, butylene oxide or styrene oxide, preferablypropylene oxide units.

The proportion of such "mixed polyether segments" may in specific casesbe accompanied by specific advantages.

Examples of the hydrophilic monohydric alcohols which are suitable inaccordance with the invention include compounds of the formulaH--X--Y--R", in which X, Y and R" have the meaning just mentioned.

These monohydric, hydrophilically modified alcohols can be prepared bythe methods described in U.S. Pat. Nos. 3,905,929 or 3,920,538, forexample by the alkoxylation of suitable starter molecules, for examplen-butanol with ethylene oxide and if desired other alkylene oxides, forexample propylene oxide.

The isocyanate derivatives which contain carbodiimide groups, areemployed in accordance with the invention and are prepared from thestarting materials mentioned by way of example have a content of from 2to 30% by weight, preferably from 5 to 15% by weight, of carbodiimidegroups --N═C═N--, and have on average per molecule from 0.8 to 30,preferably from 1 to 25 and particularly preferably from 1.3 to 20 suchcarbodiimide groups. Their content of incorporated ethylene oxide unitspresent within polyether chains is from 0 to 25% by weight, preferablyfrom 2 to 20% by weight and particularly preferably from 5 to 15% byweight, based on solids. The hydrophilic groups mentioned are preferablypresent in the carbodiimides in amounts so as to ensure their solubilityor dispersibility in water. It is however also possible, but by no meanspreferred, to use--in addition to the chemically incorporated,hydrophilic groups mentioned--external emulsifiers which are mixed withthe carbodiimides in order to ensure their solubility or dispersibilityin water.

Examples of such emulsifiers are ethoxylated nonylphenol,polyoxyethylene, lauryl ethers or polyoxyethylene laurate, oleat orstearate, these compounds generally having from 8 to 50 oxyethyleneunits per molecule.

The fact that the carbodiimides contain the groups mentioned which areessential to the invention is ensured by the corresponding choice of thenature and proportions of the starting materials and of the degree ofcarbodiimidization. The term degree of carbodiimidization is to beunderstood here as meaning the percentage of isocyanate groups, presentin the starting isocyanates (a), which undergo the carbodiimidizationreaction. The compounds employed in accordance with the inventionpreferably have no further free isocyanate groups after theirpreparation.

The compounds employed in accordance with the invention can be preparedby different variants.

The most simple method of preparation comprises reacting mixtures oforganic polyisocyantes sic!, preferably diisocyanates, with completecarbodiimidization of the isocyanate groups, polyether alcohols oralcohols containing ethylene oxide units also being employed in aquantity such that the resulting product has a content of ethylene oxidegroups which is within the abovementioned limits, and the proportion ofpolyisocyanate to monoisocyanate, i.e. the average functionality of theisocyanate mixture, being chosen such that chain termination takes placeduring the carbodiimidization reaction, so that the resulting productshave a content of carbodiimide groups which is within the abovementionedranges.

Chain termination of this kind always occurs when the average NCOfunctionality is less than 2.0. Thus by simply choosing the average NCOfunctionality of the isocyanates employed as component (a) it ispossible to adjust the molecular weight and thus the number ofcarbodiimide groups present on average in the process products.

According to a further variant only some of the isocyanate groups ofstarting component (a) are carbodiimidized, and the free isocyanategroups which are then still present are reacted with groups which arereactive towards isocyanate groups, of the kind mentioned above by wayof example under (b), the degree of carbodiimidization of the firststage of the reaction being chosen such that the quantity ofcarbodiimide groups present in the ultimate process product obtainedcorresponds to the statements made above. In this context the quantityof component (b) is always such that, for each isocyanate group of thepartially carbodiimidized isocyanate, at least 1 group which is reactivetowards isocyanate groups is available.

The number of carbodiimide groups present on average in the processproducts can also in this context be predetermined by a suitable choiceof the functionality of the starting components, i.e. by adjusting themolecular weight as is possible in this way. If, for example, the numberof carbodiimide groups in the partially carbodiimidized isocyanate hasalready been reached, then a chain-lengthening reaction will be avoidedin the reaction with component (b), i.e. exclusively chain-terminatingstructural components of the type mentioned by way of example will beused as component (b). Conversely, if at least a proportion ofdifunctional structural components (b) is used, a chain lengtheningreaction can be induced by means of which, of course, on average thenumber of carbodiimide groups present per molecule in the processproducts is increased.

In this varianat sic! of the process component (a) preferably possessesprior to the carbodiimidization reaction an NCO functionality of from1.8 to 2.5. Using this procedure it is also possible to prepare valuableprocess products which have a multiplicity of carbodiimide units,corresponding on average to the statements made above with respect tothe number of carbodiimide units.

The ethylene oxide units which may if desired be present in the processproducts are also incorporated into the process product, in the secondvariant of the preparation process, by the additional use of components(a) containing ethylene oxide units and/or by the additional use ofcomponents (b) which contain ethylene oxide units and are of the kindmentioned above by way of example.

In both variants of the process the at least partial carbodiimidizationof the isocyanate groups of component (a) is carried out in a mannerknown per se, for example in analogy with the previously known teachingof the prior art, as is evident for example from U.S. Pat. Nos.2,840,589, 2,941,966 or German Offenlegungsschriften 25 04 400, 25 52350 or 26 53 120. The at least partial carbodiimidization of theisocyanate groups of component (a) is carried out particularlyadvantageously using carbodiimidization catalysts as are described, forexample, in U.S. Pat. Nos. 2,941,966, 2,853,581 or 2,853,473 or inDE-A-26 14 323. The carbodiimidization is particularly preferablycarried out using 1-methyl-1-phospha-2-cyclopentene 1-oxide or1-methyl-1-phospha-3-cyclopentene 1-oxide or mixtures of these compoundsas catalysts.

It is of course also possible to use any other carbodiimidizationcatalysts. The at least partial carbodiimidization of component (a) iscarried out in general using from 0.01 to 5% by weight, preferably from0.2 to 2% by weight, based on component (a), of carbodiimidizationcatalysts of the type mentioned, within the temperature range from 0° to200° C., preferably 20°-150° C. If the desire is for only a partialcarbodiimidization of the isocyanate groups of component (a) it isrecommended to terminate the carbodiimidization reaction at theparticular degree of carbodiimidization required, by adding a catalystpoison. Examples of suitable catalyst poisons are described in DE-A-2614 323.

In order to obtain partially carbodiimidized isocyanates which arestorage-stable at room temperature it may be advisable to carry out thecarbodiimidization reaction at 50°-200° C. with the specific use ofcatalysts which only contain sic! their catalytic activity in thisincreased temperature range. This is described, for example, in EP-B-198343.

The progress of the carbodiimidization reaction can be monitored via theevolution of carbon dioxide and the drop in the NCO content of thereaction mixture. The partial carbodiimidization generally does notproduce uniform process products, but mixtures of carbodiimides withdifferent contents of carbodiimide units per molecule and possibly stillcontaining unreacted starting isocyanate.

All statements made above with regard to the content of carbodiimidegroups in the process products and with regard to the number ofcarbodiimide groups per molecule therefore relate to average values.

The carbodiimidization reaction can be carried out in the presence orelse in the absence of solvents. Examples of suitable solvents aretoluene, xylene, cyclohexane, chlorobenzene, O-dichlorobenzene sic!,dimethylformamide, perchloroethylene, ethyl acetate, butyl acetate,diethylene glycol dimethyl ether, tetrahydrofuran, acetone, methyl ethylketone, cyclohexanone or any desired mixtures of such solvents. Thesolvent-free carbodiimidization product prepared solidifies to give ahard resin which is ground down to a powder and is subsequently used inaccordance with the invention or can be processed further by reactionwith component (b).

The reaction with component (b) which is possibly still to be carriedout following the carbodiimidization reaction likewise takes place inthe presence or in the absence of solvents of the type mentioned by wayof example, within a temperature range of from 0° to 150°, preferablyfrom 20° to 100° C.

In this context, when using different components (b), the reactioncomponents can be reacted either simultaneously or in succession, theratio of the isocyanate groups of the carbodiimidized component (a) tothe groups of component (b) which are reactive towards isocyanate groupsbeing from 1:1 to 1:1.5, preferably from 1:1 to 1:2.

Particularly preferred is a procedure which comprises carrying out thecarbodiimidization reaction up to a degree of carbodiimidization suchthat, in the process product ultimately obtained, the required amount ofcarbodiimide groups is present. The product thus obtained is reactedwith compounds (b) which contain ethylene oxide units and which may bedifunctional, while observing a ratio of equivalents of NCO groups togroups which are reactive towards NCO groups of from 1.05:1 to 10:1, andsubsequently reacting the free NCO groups which are then still presentwith chain terminators of the type mentioned by way of example under(b), while observing a ratio of equivalents of NCO groups to groupswhich are reactive towards NCO of from 1:1 to 1:1.5, preferably 1:1, orwith a high excess of chain lengthening agents of the type describedunder (b), preferably while maintaining a ratio of equivalents of NCOgroups to groups which are reactive towards NCO groups of at least 1:2,to give an NCO-free product.

Substantially equivalent to this particularly preferred procedure wouldbe a procedure which comprises reacting the partially carbodiimidizeddiisocyanates having a mixture of difunctional hydrophilic structuralcomponents with chain terminators, while maintaining a ratio ofequivalents of NCO groups to groups which are reactive to NCO groups offrom 1:1 to 1:1.5.

After the reaction the solvent which may also have been used can beremoved, for example by distillation. The solvent-free reaction productis generally a solid which can be taken up at any time in an organicsolvent or else can be used in accordance with the invention withoutusing solvents. For this purpose the carbodiimides can be added to thecoating compositions in the form of aqueous solutions or dispersions, orelse in bulk.

If desired, after introducing ethylene oxide and/or propylene oxideunits, it is also possible for example to employ the carbodiimidesdescribed in DE-A-41 26 359, especially on page 2, line 1 to page 3,line 45.

The carbodiimides employed in accordance with the invention areparticularly suitable for modifying polyurethane which containscarboxylate and/or carboxyl groups and/or sulfonate groups and ispresent in dispersion or dissolved in water, and for modifying polyesterresins, polybutadienes or polyacrylate resins which are present indispersion or dissolved in water and contain carboxylate groups and/orcarboxyl groups and/or sulfonate groups.

The quantity of the carbodiimides employed in accordance with theinvention depends, on the one hand, on the content of carboxylate groupsand/or carboxyl groups in the dissolved or dispersed polymer and, on theother hand, on the desired range of properties of the coatings. Forinstance it may on the one hand be desired to select the ratio ofcarboxylate groups and/or carboxyl groups and/or sulfonate groups in thedissolved or dispersed binder to the carbodiimide groups so as to begreater than 1:1 in order, especially when using carbodiimides havingmore than 2 carbodiimide groups per molecule, to prevent excessivecrosslinking of the product; on the other hand the use of at leastequivalent amounts of carbodiimide groups, especially carbodiimideswhich (on average) are at least difunctional, enables the reaction timeduring the drying of the coatings ultimately obtained to be shortened.

Furthermore, the coating compositions according to the invention maycontain as additive, together with or instead of the carbodiimides, apolyepoxide component (D). Examples of suitable polyepoxides are allknown aliphatic and/or cycloaliphatic and/or aromatic polyepoxides,based for example on bisphenol A or bisphenol F.

Suitable examples of component (D) include the polyepoxides which arecommercially available under the names Epikote® from Shell, Denacol fromNagase Chemicals Ltd., Japan, for example Denacol Ex-411(pentaerythritol polyglycidyl ether), Denacol EX-321 (trimethylolpropanepolyglycidyl ether), Denacol EX-512 (polyglycerol polyglycidyl ether)and Denacol EX-521 (polyglycerol polyglycidyl ether).

In the coating compositions according to the invention the polyepoxidecomponent (D) is preferably employed in an amount such that the weightratio of binder solids to polyepoxide solids is between 60:40 and 90:10,preferably between 70:30 and 85:15.

In order to prepare the ready-to-use, aqueous polyurethane coatingcomposition, a mixture of polyisocyanate component (B) and carbodiimidecomponent (C) and/or of polyepoxide component (D) is mixed shortlybefore application with binder component (A). The components can bemixed simply by stirring them together at room temperature or else bydispersion. The polyisocyanate component (B) is here employed in anamount such that the weight ratio between binder solids andpolyisocyanate solids is from 60:40 to 90:10, particularly preferablyfrom 70:30 to 85:15. The ratio of the number of free OH groups ofcomponent (A) to the number of isocyanate groups of component (B) isusually in the range from 1:2 to 2:1 in this context.

It is preferred to employ the carbodiimide component in an amount suchthat the weight ratio between binder solids (A) and carbodiimide solids(C) is between 60:40 and 90:10, preferably between 70:30 and 85:15. Theratio of the number of acid groups of binder (A) to the carbodiumidegroups of component (C) is usually in the range between 1:2 and 2:1 inthis context.

The aqueous polyurethane resin coating compositions according to theinvention may also contain, in addition to the polyaddition and/orpolycondensation resin employed in accordance with the invention,crosslinked polymer microparticles as disclosed in, for example, EP-A-38127, and/or further compatible resins such as, for example,water-dilutable or water-soluble polyacrylate resins, polyurethaneresins, polyester resins, alkyd resins or epoxy resin esters. Theproportion of these further resins is usually between 1 and 10% byweight, based on the total weight of the coating composition. Forinstance, up to 30% by weight based on the binder solids of an acrylateprepared by emulsion polymerization and having an OH number which ispreferably between 40 and 200 mg of KOH g may be added to the coatingcompositions according to the invention. The preparation of suchemulsion polymers is described in, for example, DE-A-40 09 000, althoughthe OH number of the acrylates is to be raised correspondingly.

Over and above this, the coating compositions according to the inventionmay also contain other conventional auxiliaries and additives such as,in particular, thickeners and wetting agents. It is preferred to add tothe aqueous coating compositions according to the invention a nonionicpolyurethane thickener, since this leads to a better transparency andbetter emulsifiability of the polyisocyanate. Preferably, the aqueouscoating compositions according to the invention also have added to thema wetting agent based on an alkyl-modified polyether, since thislikewise improves the transparency of the coating composition and thegloss and levelling of the coating composition.

Furthermore the aqueous coating compositions may also contain otherconventional auxiliaries and additives, for example antifoams and thelike. The quantity of auxiliaries and additives (incl. wetting agentsand thickeners) employed is conventionally between 1 and 5% by weight,based on the total weight of the coating compositions.

The aqueous coating compositions according to the invention may alsocontain conventional organic solvents, whose proportion is kept as lowas possible. This proportion is conventionally below 15% by weight,based on the total content of the volatile constituents.

The coating compositions according to the invention are generallyadjusted to a pH of between 6.5 and 9.0. The pH can be adjusted usingconventional amines such as, for example, triethylamine,dimethylaminoethanol and N-methylmorpholine.

The coating compositions according to the invention can be applied usingconventional application methods such as, for example, spraying, knifecoating, brushing, dipping, to any desired substrates such as, forexample, metal, wood, plastic or paper. The coating compositionsaccording to the invention are preferably employed for the production oftop coats. The coating compositions according to the invention can beemployed both in the production-line finishing and in the refinishing ofcar bodies. They are, however, preferably employed in the refinishingsector. The aqueous coating compositions according to the invention canbe employed as fillers and for producing one-coat top coats, and aspigmented basecoats or as clearcoats in a process for the production ofa multilayer finish (basecoat/clearcoat method). The coatingcompositions according to the invention are, however, preferablyemployed as clearcoats.

If the coating compositions according to the invention are employed forthe production of single-coat top coats or as basecoats, then they canbe pigmented with pigments such as, for example, pigments with aninorganic basis, for example titanium dioxide, iron oxide, carbon blacketc. and/or pigments with an organic basis and/or metallic pigments suchas, for example, aluminum bronzes, and/or pearlescent or interferencepigments. Aluminum bronzes and pearlescent or interference pigments areexamples of special-effect pigments. If the coating compositionsaccording to the invention are employed as pigmented basecoats then theycan be covered over with the coating compositions according to theinvention which contain no pigments or only transparent pigments,although they can also be covered with conventional clearcoats based onorganic solvents, with aqueous clearcoats or else with powderclearcoats.

The top coat compositions according to the invention

have a solids content at spray viscosity which is high enough (20 to 50%by weight, preferably 32 to 45% by weight) to obtain, with 1 to 2 spraypasses (cross passes), coating films of adequate thickness (thethickness of the baked coating film should preferably be between 25 and70 μm) and

give coating films having a very good appearance (good evenness, highgloss, good top coat holdout), good weathering resistance and goodmechanical properties, and

have a relatively low content of organic cosolvents (less than 35% byweight based on the total solids content of binders and crosslinkingagents).

If the top coat compositions according to the invention are usedtogether with water-dilutable base coat compositions in order to producemetallic finishes, then in the metallic finishes obtained thetransparent top coat adheres particularly well to the basecoat. Suitablebasecoats are, for example, the aqueous basecoat described in DE-A-40 09000. Also suitable are all conventionally employed aqueous basecoats.

The following examples describe the invention in more detail. All partsand percentages are by weight unless expressly stated otherwise.

EXAMPLES 1 TO 4 Comparative Examples 1 and 2

1. Preparation of a water-dilutable acrylate resin employed inaccordance with the invention (A1)

24 parts by weight of ethoxyethyl propionate (EP) are introduced into asteel vessel fitted with monomer feed, initiator feed, thermometer, oilheating and reflux condenser and heated to 120° C. Then a solution of6.0 parts by weight of t-butyl perethylhexanoate in 6.0 parts by weightof ethoxyethyl propionate is added at a rate such that the addition isconcluded after 4 h 30 min. The commencement of the addition of thet-butyl perethylhexanoate solution is accompanied by the beginning ofthe addition of the monomer mixture of (a1), (a2), a3) and (a4)

(a1): 20.0 parts by weight of n-butyl methacrylate 17.4 parts by weightof methyl methacrylate, 10.0 parts by weight of lauryl acrylate(commercial product Methacrylester 13 from Rhoim AG, Darmstadt)

(a6): 15.0 parts by weight of styrene

(a2): 32.5 parts by weight of hydroxyethyl methacrylate

(a3): 5.1 parts by weight of acrylic acid.

The mixture (a1), (a2), (a3) and (a6) is added at a rate such that theaddition is concluded after 4 hours. When the addition of the t-butylperethylhexanoate solution is over the reaction mixture is maintained at120° C. for a further 2 h. The resin solution is then cooled to 80° C.and neutralized over a period of about 30 min with dimethylethanolamine,to a degree of neutralization of 60 %.

Then a quantity of water is added until the solids content of thedispersion is about 40% by weight. Organic solvent is removed byazeotropic distillation under vacuum from this dispersion until no morethan 3% can be detected (by GC). Whereas the organic solvent was sic!separated off, the water is returned to the reactor.

At the end of the distillation the dispersion is adjusted, by addingdeionized water, to the following final parameters:

Acid number of the total solids: 40 mg of KOH/g of solids;

OH number of the total solids: 140 mg of KOH/g of solids;

solids content (1 h, 130° C): 39.0%.

2.1 Preparation of a carbodiimide 1 employed in accordance with theinvention (C1)

475 parts of (1,3-bis(2-isocyanatoprop-2-yl)benzene (commercial productTMXDI (Meta)® from American Cynamid sic! Comp.) and 119 g of isophoronediisocyanate together with 14 parts of 3-methyl-1-phenyl-2-phospholene1-oxide are placed in a reactor. They are heated under a nitrogenatmosphere at 155° C. until the isocyanate content has reached 6.5%(approximately after 19 h). The reaction mixture is then cooled to 50°C. before 143 parts of methoxy polyethylene glycol having a molecularweight of 550 and 0.6 parts of dibutyl tin dilaurate are added. Themixture is stirred at 50° C. until a constant isocyanate content ofabout 4.2% has been reached. Then at 50° C. 142 parts of ethanol areadded and the mixture is stirred until no free NCO is determined.

The remaining ethanol is distilled off under vacuum and the batch isdiluted with metoxypropyl sic! acetate to a solids content of 79%.

2.2 Preparation of the carbodiimide 2 employed in accordance with theinvention

50 parts of a tetraisopropyldiphenyl-methanecarbodiimide (preparedaccording to DE-A 41 26 359), in which the remaining NCO groups had beenpartially urethanized with ethanol (8% free NCO groups) were reactedwith 25 parts of a commercially available polyether alcohol of thepropylene glycol type having an average molecular weight of 900(commercial product Pluriol® P 900 from BASF AG) and 0.1 parts ofdibutyl tin dilaurate (DBTL) for 6 hours at 80° C. The solids contentwas adjusted to 60% using methoxypropyl acetate and the product wasdrained off.

3.) Preparation of transparent aqueous top coat compositions accordingto the invention

Transparent top coat compositions are prepared from the acrylatedispersion prepared according to point A, an 80% strength solution of acommercially available water-dilutable polyisocyanate resin in ethylethoxypropionate, based on hexamethylene diisocyanate dimer/trimer,containing uretdione groups (commercial product Desmodur® N 3400 fromBayer AG), if desired the carbodiimide 1 or 2, if desired a commerciallyavailable aromatic polyepoxide having an epoxide equivalent weight of231 (commercial product Denacol EX-411 from Nagase Chemical Ltd.,Japan), butylglycol, methyl isobutyl ketone, ethoxyethyl propionate, a10% strength aqueous solution of a commercially available polyurethanethickener (Dapral T 210 from Akzo), distilled water, a commerciallyavailable siloxane-modified surface additive (commercial product TegoFlow 425 from Goldschmidt, Essen) and a surface-active agent based onsilicone (commercial product Byk 331 from Byk), and these compositionsare adjusted using distilled water to spray viscosity (22 to 25 s effluxtime from the DIN-4 cup (in accordance with DIN 53 211, 1974)). Thecomposition of the top coat compositions is shown in Table 1.

4.) Application of the transparent top coat compositions according tothe invention and testing of the baked coating films

A water-dilutable basecoat composition pigmented with aluminum flakes,according to EP-A-279 813, is applied to a phosphatized steel panelcoated with a commercially available electrodeposition coating and acommercially available filler so as to give a dry film thickness of from12 to 15 μm. The applied basecoat composition is dried for 10 min atroom temperature and 10 min at 60° C. A top coat composition obtained asin point B) is then sprayed onto the basecoat in 3 spray passes with aflashoff time of 15 min in between. The panel is finally dried for 60min at room temperature and baked for 30 min at 60° C. in acirculating-air oven. The resulting multilayer coatings were subjectedto a number of tests. The test results are shown in Table 2.

                  TABLE 2                                                         ______________________________________                                        Composition of the transparent, aqueous top coat compositions                 from Examples 1 to 3 and Comparative Examples 1 and 2                                                            Com-  Com-                                                                    parative                                                                            parative                                    Exam- Exam-   Exam-   Exam- Exam- Exam-                                       ple 1 ple 2   ple 3   ple 4 ple 1 ple 2                                ______________________________________                                        Acrylate 56.6    56.1    56.1  56.1  58.0  60.0                               dispersion                                                                    Distilled                                                                              5.7     5.6     5.6   5.6   5.9   6.0                                water                                                                         Daspral T210                                                                           1.4     1.4     1.4   1.4   1.4   1.4                                (10%)                                                                         Butyl glycol                                                                           1.1     1.1     1.1   1.1   1.1   1.1                                Methyl isobutyl                                                                        1.1     1.1     1.1   1.1   1.1   1.1                                ketone                                                                        Ethoxyethyl                                                                            2.3     2.3     2.3   2.3   2.3   2.3                                propionate                                                                    Byk 331  0.1     0.1     0.1   0.1   0.1   0.1                                Tego Flow 425                                                                          0.1     0.1     0.1   0.1   0.1   0.1                                Distilled water                                                                        2.3     2.2     2.2   2.2   2.3   2.3                                Desmodur 13.0    12.9    12.9  12.9  13.5  --                                 N3400                                                                         Carbodiimide 1                                                                         1.1                                                                           1.1                                                                           7.0                                                                  Carbodiimide 2                                                                         --      1.2                                                          Denacol  --                                                                            1.0     2.8                                                          EX-411                                                                        Ethoxyethyl                                                                            3.2     3.2     3.2   3.2   3.2   6.1                                propionate                                                                    Distilled water                                                                        12.0    12.7    11.8  11.1  11.0  12.5                               Solids content                                                                         40      39      41    41    39    39                                 (%)                                                                           Solvent (%)                                                                            12.2    12.2    12.0  12.0  12.0  14.0                               Viscosity (DIN                                                                         23      22      23    24    25    22                                 4 cup)s                                                                       ______________________________________                                    

                                      TABLE 2                                     __________________________________________________________________________    Test results                                                                           Example 1                                                                             Example 2                                                                             Example 3                                                                             Example 4                                                                             Comp. Ex. 1                                                                           Comp. Ex.2                            before after                                                                          before after                                                                          before after                                                                          before after                                                                          before after                                                                          before after                          Exposure                                                                              Exposure                                                                              Exposure                                                                              Exposure                                                                              Exposure                                                                              Exposure                     __________________________________________________________________________    Solids content.sup.1)                                                                  40%     39%     41%     41%     39%     39%                          Coat thickness                                                                         50      50      50      50      50      50                           (lm).sup.2)                                                                   CC test.sup.3) (3 days)                                                       Blistering                                                                             m0/g0                                                                             m1/g1                                                                             m0/g0                                                                             m2/g1                                                                             m0g/0                                                                             m1/g1                                                                             m0/g0                                                                             m2/g1                                                                             m0/g0                                                                             m2/g2                                                                             m0/g0                                                                             m3/g3                    Swelling 0   4   0   4   0   2   0   4   0   5   0   5                        Cratering                                                                              0   0   0   0   0   0   0   0-1 0   1   0   1                        CC test.sup.3) (10 days)                                                      Blistering                                                                             m0/g0                                                                             m2/g1                                                                             m0/g0                                                                             m3/g3                                                                             m0/g0                                                                             m2/g1                                                                             m0/g0                                                                             m3/g3                                                                             m0/g0                                                                             m4/g3                                                                             m0/g0                                                                             m5/g3                    Swelling 0   5   0   5   0   3   0   5   0   5   0   5                        Cratering                                                                              0   0   0   0   0   0   0   1   0   2   0   3                        WS test.sup.4) (5 cycles)                                                     Blistering                                                                             m0/g0                                                                             m0/g0                                                                             m0/g0                                                                             m0/g0                                                                             m0/g0                                                                             m0/g0                                                                             m0/g0                                                                             m1/g1                                                                             m0/g0                                                                             m1/g1                                                                             m0/g0                                                                             m3/g2.sup.4)             Swelling 0   2-3 0   2-3 0   1-2 0   3   0   3-4 0   4.sup.4)                 Pendulum hardness                                                             Konig RT 105     97      118     119     103     55                           30' 60° C.                                                                      126     120     145     148     126     74                           __________________________________________________________________________

We claim:
 1. Aqueous multicomponent polyurethane coating compositioncomprisingA) a water-dilutable resin selected from the group consistingof polyaddition resin (A1), polycondensation resin (A2), and mixturesthereof, wherein the resin contains groups selected from the groupconsisting of hydroxyl, carboxylate, and sulfonate groups, and mixturesthereof, and having an OH number of from 40 to 200 mg of KOH/g, an acidnumber of from 15 to 100 mg of KOH/g, and a glass transition temperatureof from -40° C. to +60° C. B) a polyisocyanate component (B) ascrosslinking agent and at least one additive, selected from the groupconsisting of a carbodiimide component (C), a polyepoxide component (D)and mixtures thereof,wherein the carbodiimide component (C) has acontent of carbodiimide groups --N═C═N-- of from 2 to 30% by weight, onaverage at least 0.8 carbodiimide groups per molecule and from 0 to 25%by weight, based on solids, of chemically incorporated ethylene oxideand/or propylene oxide units which are present within polyether chains.2. Coating composition according to claim 1, wherein carbodiimidecomponent (C) is contained in an amount such that the weight ratio ofbinder component (A) to carbodiimide (C) is between 90:10 and 60:40. 3.Coating composition according to claim 1, wherein the carbodiimidecomponent has a content of carbodiimide groups --N═C═N-- of from 5 to15% by weight, on average from 1 to 25 carbodiimide groups per moleculeand from 2 to 20% by weight, based on solids, of chemically incorporatedethylene oxide and/or propylene oxide units present within polyetherchains.
 4. Coating composition according to claim 1 wherein carbodiimidecomponent (C) has been prepared by reacting at least one compoundselected from the group consisting of aliphatic diisocyanates,cycloaliphatic di-isocyanates, aliphatic polyisocyanates, aromaticpolyisocyanates and mixtures thereof, with alcohols containing ethyleneoxide and/or propylene oxide units.
 5. Coating composition according toclaim 4, wherein carbodiimide component (C) has been prepared usingtetramethylene-xylylenediisocyanate as the sole isocyanate component. 6.Coating composition according to claim 1, wherein the additive is acarbodiimide component (C).
 7. Coating composition according to claim 1,wherein polyepoxide component (D) is selected from the group consistingof aliphatic, cycloaliphatic and aromatic polyepoxides and mixturesthereof.
 8. Coating composition according to claim 1, wherein bindingcomponent (A) is a water-dilutable polyacrylate resin (A1) which isobtained by polymerizing, in an organic solvent or solvent mixture andin the presence of at least one polymerization initiatora1) a(meth)acrylate which is different from (a2), (a3), (a4), (a5) and (a6),is copolymerizabhe with (a2), (a3), (a4), (a5) and (a6) and isessentially free from carboxyl groups, or a mixture of such monomers,a2) an ethylenically unsaturated monomer which is copolymerizable with(a1), (a3), (a4), (a5) and (a6), is different from (a5), carries atleast one hydroxyl group per molecule and is essentially free fromcarboxyl groups, or a mixture of such monomers, a3) an ethylenicallyunsaturated monomer which carries at least one carboxyl group permolecule and is copolymerizable with (a1), (a2), (a4), (a5) and (a6), ora mixture of such monomers, andoptionally compounds a4)-a6) selectedfrom the group consisting of a4) one or more vinyl esters of -branchedmonocarboxylic acids having from 5 to 18 carbon atoms per molecule, a5)compounds selected from the group consisting of(i) at least one reactionproduct of acrylic acid and/or methacrylic acid with the glycidyl esterof an α-branched monocarboxylic acid having from 5 to 18 carbon atomsper molecule, and (ii) an equivalent amount of acrylic and/ormethacrylic acid which is reacted during or after the polymerizationreaction with the glycidyl ester of an -branched monocarboxylic acidhaving from 5 to 18 carbon atoms per molecule, and a6) an ethylenicallyunsaturated monomer which is copolymerizable with (a1), (a2), (a3), (a4)and (a5), is different from (a1), (a2), (a3), (a4) and (a5) and isessentially free from carboxyl groups, or a mixture of suchmonomers,and, after the end of the polymerization, at least partiallyneutralizing the resulting polyacrylate resin and dispersing it inwater, the nature and quantity of (a1), (a2), (a3), (a4), (a5) and (a6)being selected such that the polyacrylate resin (A1) has the desired OHnumber, acid number and glass transition temperature.
 9. Aqueous coatingcomposition according to claim 8, wherein water-dilutable polyacrylateresin (A1) is obtained by(I) polymerizing a mixture of (a1), (a2), (a4),(a5) and (a6), or a mixture of part-amounts of components (a1), (a2),(a4), (a5) and (a6) in an organic solvent, (II) after at least 60% byweight of the mixture composed of (a1), (a2), (a4), (a5) and if desired(a6) have been added, adding (a5) and any remaining amount of components(a1), (a2), (a4), (a5) and (a6) and continuing polymerization, and (III)after the end of the polymerization, at least partially neutralizing theresulting polyacrylate resin and dispersing it in water.
 10. Aqueouscoating composition according to claim 8, wherein component (a2)comprises trimethylolpropane monoallyl ether.
 11. Aqueous coatingcomposition according to claim 1, wherein water-dilutable polyacrylateresin (A1) is obtained from(a1) from 30 to 50% by weight, of component(a1) (a2) from 15 to 35% by weight, of component (a2) (a3) from 2 to 8%by weight, of component (a3) (a4) from 2 to 15% by weight, of component(a4) (a5) from 2 to 15% by weight, of component (a5) and (a6) from 10 to20% by weight, of component (a6), the sum of the proportions by weightof components (a1) to (a6) being in each case 100% by weight. 12.Process for the preparation of an aqueous multicomponent polyurethanecoating composition according to claim 1 wherein shortly beforeapplication the isocyanate group-containing crosslinking agent, theadditive and the water-dilutable resin (A) are mixed.
 13. Processaccording to claim 12, wherein shortly before application a crosslinkingcomponent (I) which contains the isocyanate group-containingcrosslinking agent, the additive, and a binder component (II) whichcontains the water-dilutable resin (A), are mixed.
 14. Method ofproducing a multilayer, coating on a substrate surface, comprising(1)applying a pigmented basecoat composition to the substrate surface, (2)forming a polymer film from the composition applied in stage (1), (3)applying a transparent aqueous top coat composition comprising awater-dilutable polyacrylate resin binder and a polyisocyanatecrosslinking agent to the resulting basecoat, and subsequently (4)curing the basecoat together with the top coat,wherein the top coatcomposition applied is an aqueous coating composition according toclaim
 1. 15. Article coated with a multicoat finish, wherein one of thecoats has been produced using an aqueous coating composition accordingto claim
 1. 16. An automotive refinish top coat comprising the aqueousmulticomponent polyurethane coating composition of claim
 1. 17. Coatingcomposition according to claim 1, wherein the polyepoxide component (D)is contained in an amount such that the weight ratio of binder component(A) to polyepoxide (D) is between 85:15 and 70:30, the weight ratiosbeing based in each case on solids.
 18. Coating composition according toclaim 1, wherein carbodiimide component (c) is contained in an amountsuch that the weight ratio of binder component (A) to carbodiimide (C)is between 85:15 and 70:30, the weight ratios being based in each caseon solids.
 19. Coating composition according to claim 1, wherein theadditive is a mixture of a carbodiimide component (C) and a polyepoxidecomponent (D).
 20. Aqueous coating composition according to claim 8wherein component (a4) comprises one or more vinyl esters of -branched,saturated aliphatic monocarboxylic acids having from 9 to 11 carbonatoms.
 21. Aqueous coating composition according to claim 8 whereincomponent (a5) comprises a compound selected from the group consistingof the reaction product of acrylic and/or methacrylic acid with theglycidyl ester of Versatic acid, an equivalent amount of acrylic and/ormethacrylic acid which is then reacted during or after thepolymerization reaction with the glycidyl ester of Versatic acid. 22.Aqueous coating composition according to claim 20 wherein component (a5)comprises a compound selected from the group consisting of the reactionproduct of ((meth)acrylic acid with the glycidyl ester of Versatic acid,and an equivalent amount of (meth)acrylic acid which is then reactedduring or after the polymerization reaction with the glycidyl ester ofVersatic acid.
 23. An aqueous multicomponent polyurethane coatingcomposition comprisingA) a water-dilutable resin selected from the groupconsisting of polyaddition resin (A1), polycondensation resin (A2), andmixtures thereof, wherein the resin contains groups selected from thegroup consisting of hydroxyl, carboxylate, and sulfonate groups, andmixtures thereof, and having an OH number of from 40 to 200 mg of KOH/g,an acid number of from 15 to 100 mg of KOH/g, and a glass transitiontemperature of from -40° C. to +60° C. B) a polyisocyanate component (B)as crosslinking agent andat least one additive comprising a carbodiimidecomponent (C)having a content of carbodiimide groups --N═C═N-- of from 2to 30% by weight, on average at least 0.8 carbodiimide groups permolecule and from 2 to 25% by weight, based on solids, of chemicallyincorporated ethylene oxide and/or propylene oxide units which arepresent within polyether chains.
 24. An aqueous multicomponentpolyurethane coating composition comprisingA) a water-dilutable resinselected from the group consisting of polyaddition resin (A1),polycondensation resin (A2), and mixtures thereof, wherein the resincontains groups selected from the group consisting of hydroxyl,carboxylate, and sulfonate groups, and mixtures thereof, and having anOH number of from 40 to 200 mg of KOH/g, an acid number of from 15 to100 mg of KOH/g, and a glass transition temperature of from -40° C. to+60° C., which is obtained by polymerizing, in an organic solvent orsolvent mixture and in the presence of at least one polymerizationinitiator:a1) a (meth)acrylate which is different from (a2), (a3), (a4),(a5) and (a6), is copolymerizable with (a2), (a3), (a4), (a5) and (a6)and is essentially free from carboxyl groups, or a mixture of suchmonomers, a2) an ethylenically unsaturated monomer which iscopolymerizable with (a1), (a3), (a4), (a5) and (a6), is different from(a5), carries at least one hydroxyl group peer molecule and isessentially free from carboxyl groups, or a mixture of such monomers,a3) an ethylenically unsaturated monomer which carries at least onecarboxyl group per molecule and is copolymerizable with (a1), (a2),(a4), (a5) and (a6), or a mixture of such monomers, andoptionallycompounds a4)-a6) selected from the group consisting of a4) one or morevinyl esters of -branched monocarboxylic acids having from 5 to 18carbon atoms per molecule, a5) compounds selected from the groupconsisting of(i) at least one reaction product of acrylic acid and/ormethacrylic acid with the glycidyl ester of an α-branched monocarboxylicacid having from 5 to 18 carbon atoms per molecule, and (ii) anequivalent amount of acrylic and/or methacrylic acid which is reactedduring or after the polymerization reaction with the glycidyl ester ofan -branched monocarboxylic acid having from 5 to 18 carbon atoms permolecule, and a6) an ethylenically unsaturated monomer which iscopolymerizable with (a1), (a2), (a3), (a4) and (a5), is different from(a1), (a2), (a3), (a4) and (a5) and is essentially free from carboxylgroups, or a mixture of such monomers,and, after the end of thepolymerization, at least partially neutralizing the resultingpolyacrylate resin and dispersing it in water, the nature and quantityof (a1), (a2), (a3), (a4), (a5) and (a6) being selected such that thepolyacrylate resin (A1) has the desired OH number, acid number and glasstransition temperature, B) a polyisocyanate component (B) ascrosslinking agent, and at least one additive, selected from the groupconsisting of a carbodiimide component (C), a polyepoxide component (D)and mixtures thereof, wherein the carbodiimide component (C) has acontent of carbodiimide groups --N═C═N-- of from 2 to 30% by weight, onaverage at least 0.8 carbodiimide groups per molecule and from 0 to 25%by weight, based on solids, of chemically incorporated ethylene oxideand/or propylene oxide units which are present within polyether chains.